Telecommunications systems employing time division switching are, of course, well-known in the art. Such systems have employed many different approaches, the most prevalent being those which allocate each time slot to a conversation path. Where systems assign a time channel to each function circuit, all activities relative to the call in process over a channel are generally consummated during that channel period. Frequently, this processing is accomplished by subdividing the channel period into individual sub-periods for each step in the sequence. Thus, the duration of each time slot must be lengthened to provide the serial transmission of data.
Other systems combine both time division and space division to provide sufficient time slots and line capacity. Still other systems employ a single closed loop and transmit information on the loop only as from one line to another line, each line having a fixed time slot appearance on the line.
Within the general framework of TDM switching, either one of two basic approaches have been used, these being the single highway and the dual highway approaches. With a single highway, allocation of channels for each direction of transmission is necessary while the dual highway provides unidirectional flow of information with the necessity of synchronizing and maintaining synchronization of channels.